What should a driver avoid doing when there are no passengers on the bus?

When there are no passengers on the bus, it is still essential for the driver to adhere to safety regulations and maintain professional conduct. Smoking is particularly problematic because it can create unpleasant odors and health hazards. Additionally, it can be seen as unprofessional and might violate certain regulations or company policies related to cleanliness and health standards on public transportation vehicles.

While the other options also represent unsafe or inappropriate behaviors that a driver should avoid, the act of smoking specifically poses immediate health concerns and can adversely affect the environment inside the vehicle, even when empty. Thus, avoiding smoking is crucial for maintaining a clean and safe atmosphere for passengers and ensuring compliance with health regulations.